Production of aromatic hydrocarbons



July l, 1947. R, M COLE PRDUCTION OF AROMATIC HYDROCARBONS Filed Jan. 26, 1945 Invenor: Rober* M. Cole Bg his Aforneg Qg &j

Patented July 1, 1947 PRODUCTION OF AROMATIC HYDROCARBONS Robert M. Cole, Oakland, Calif., assignor to Shell Development Company, San ,lranciscm- Calif., a corporation of Delaware Application January 26, 1945, Serial No. 574,756

claims. l

This invention relates to a process for the production of aromatic hydrocarbons from cracked gasoline stocks and similar stocks containing sulfur compounds and olefins.

In my copending application, Serial No. 569,234, filed December 21, 1944, of which this application is a continuation-impart, I have described a process for the treatment of sulfur-bearinghydrocarbon fractions of the nature of cracked gasolines for the purpose of removing sulfur cornpounds therefrom. According to one preferred embodiment of said process the material is subjected to two treatments under hydrogen pressure *in the presence of sulf-active hydrogenation-dehydrogenationcatalysts, the first treatment being carried out at a temperature below about 850 F. and under such conditions that the sulfur concentration is decreased to slightly be- I I low 0.10% while leaving the olens substantially unaiected, and the second treatment being carried out at a temperature above about 850 F. in order to prevept depreciation of the anti-knock properties of the material being desulfurized. In another embodiment of the invention they desulfurization is carried out without loss of antiknock properties at temperaturesVv above about 850 F. and the sulfur content of theifeed is maintained below about 0.10% by recycling a suitable y amount of the desulfurized product. The present invention relates to a process which is designed primarily to obtain maximum production 'of 'dcsirable aromatic hydrocarbons in a relatively pure form rather than to 'desulfurization (although process thenaphthenic straight run gasplineis fractionated in a specific particular manner which cannot be divulged at this time. A part of it is subjected to a.' catalytic isomerization treatment to convert nonhydroaromatic naphthenes to the corresponding hydroaromatic naphthenes. Certain selected fractions are then subjected to catalytic dehydrogenation to convert hydroaromatic naphthenes to the corresponding aromatic hydrocarbons, and finally the aromatic hydrocarbons are recovered irl a substantially pure state by a suitable process such, for instance, as extractive distillation. As stated above, these processes are designedfor and are suitable only for the production of aromatic hydrocarbons from naphthenic straight run petroleum frac. tions. Neither process is suited for the treatment vof materials containing substantial amounts of hydrocarbons from olenic cracked stocks. Gassubstantial desulfurization is inherent), in which process various features of the invention de scribed in the above-mentioned copending appli-- cation are applied in novel combination to afford certain further advantages. l

Various processes for the production of aromatic hydrocarbons, for example, synthetic toluene and synthetic Xylene have been proposed and y two of these are presently used to produce the greater part of the nations supply of these materials. These processes are designed for and adapted only to the production of these materials from naphthenic straight run petroleum fractions,

One of these processes is a specific y application of the broader so-called hydroform-` oline and other stocks obtained by thermal cracking, thermal reforming, catalytic cracking, and certain other high temperature processes usually have the following characteristics: They contain appreciable quantities of olens aid other unsaturated bodies. They contain appreciable quanti- ,ties of aromatic hydrocarbons and naphthenes.

They contain appreciable amounts of sulfur compounds and other-impurities. The sulfur cofitent is usually in the order of 0.2% to over 1%. These. stocks n are a potential source of large amounts of a variety of aromatic hydrocarbons. However, due to the presence of the oleilns, sul-A fur compounds and other impurities the obtalnm ing of the potential aromatic hydrocarbons from such materials has been most difllcult and unecenomical. The process of thepresent invention aifords a practical and economical process for the the feed to about 0.10%, or somewhat lower, with matic naphthenes; subjecting said fraction to a catalytic isomerization treatment; and 'cycling at 15 least a portion of said isomerized material to the second hydrogen treatment( The process will be described in more detail in connection with the schematic flow diagram in the accompanying drawing. Referring to the drawing, the feed entering via line l is mixed with a suitable amount of hydrogen entering via line 2 and subjected to a partial desulfurization-hydrogenation treatment. The feed is a sulfur-bearing olefinic petroleum `fraction such as a cracked 25 gasoline fraction or the like. As pointed out.

vthese materials ordinarily contain appreciable amounts of sulfur. The treating conditions in this rst hydrogen treatment are adjusted to reduce the sulfur content of the material to about 0.10% or less or to such an extent that after adding the recycled isomerized fraction and/or some straight run naphthenic gasoline, the sulfur content of the mixture does not exceed 0.10%. For reasons set forth in the above-mentioned copending application this treatment is carried out at a temperature below about 850 F., for example at a temperature between about 450 F. and 850 F. The treatment is carried out in the presence of an excess of hydrogen, for example, 1 to 30 mols of hydrogen per mol of hydrocarbon and at'a superatmospheric pressure of at least 10 atmospheres. Any of the various sulf-'active hydrogenation catalysts may be employed. Examples of such suitable catalysts are tungsten sulfide, nickel sulfide, iron sulfide, cobalt sulfide, molybdenum sulfide, cobalt thiomolybdate, zinc chromite, and various combinations of these. Under the chosen conditions a'substantial if not the major, part of the olens in the feed remains intact.

The hydrogen gas recycled in this step tends to become enriched in hydrogen sulfide. vConsequently the hydrogen is usually recycled via line 3 to a hydrogen sulfide-removal system such a-s a Shell phosphate treater or the like. Hydrogen sulfide recovered per se or 'as a secondary product is removed via line 4. Most of the hydrogen for the treatment is usually supplied by the second hydrogen treatment. Make-up hydrogen for the 60 process is added via line 5.

A substantially saturated isomerized fraction such as hydroaromatic hydrocarbon is added via line 6 to the product from the first, or low temperature, hydrogen treatment.` If desired a 65 these conditions a further substantial desulfurization is also effected. Thus, the temperature in the second, or high temperature, treatment is between about 850 F. and 1000 F. 'I'he treatment is carried out in the presence of a large excess -of hydrogen, for example, 4 to 30 mols of hydrogen per mol of hydrocarbon, and at a superatmospheric pressure of at least 10 atmospheres. The catalyst used in this second treatment is a dehydrogenating sulfide of a metal of the ironl group and may furthermore advantageously also contain a sulfide of a metal of the group VI of the periodic system of the elements. Particularly suitable catalysts are, for example, a mixture of sulfldes of nickel and tungsten corresponding approximately to the formula and various combinations of sulfide com-pounds of cobalt and molybdenum. The first of these ls advantageously applied without a carrier and the second is advantageously applied with a carriersuch in particular as an Activated Aluminasilica blend.

The hydrogen gas used in the second step may also be recycled via line I0 through a suitable hydrogen sulfide-removal system as illustrated. The product from the second hydrogen treatment contains substantial amounts of aromatic hydrocarbons. It also contains appreciable amounts of non-hydroaromatic naphthenes which wer epresent in the original feed and/or formed in the preceding steps and which are not dehydrogenated under the present conditions specified. It is,however, substantially free of sulfur compounds and oleflns. Consequently, the recovery of aromatic hydrocarbons from this material is much less difficult than the recovery of the aromatics from the original feed. The product from the second hydrogen treatment, or a fraction thereof, is passed via line il to an aromatic hydrocarbon-recovery system to remove the aromatic hydrocarbons.- Any of the conventional systems involving solvent extraction, distillation, extractive distillation. or azeotropic distillation may be employed. The recovered aromatic hydrocarbon is removed via line l2.

The material remaining after the removal of the aromatichydrocarbons contains considerable quantities of non-hydroaromatic naphthenes such, for example, as (depending upon.the boiling range of the materials charged) methylcyclopentane, dimethylcyclopentanes, ethylcyclopentanes, methyl ethyl cyclopentane, and the like. These materials may be introduced as constituents of the original feed and/or by formation from hydroaromatic naphthenes during one or both of the hydrogen treatments. These non-hydroaromatic naphthenes, it is found, may be easily concentrated by a simple fractionation. The materialremaining after the removal of the aromatic hydrocarbon is therefore first subjected to a suitable fractionation to separate a fraction rich in one or. more of these non-hydroaromatic naphthenes. For example, if the original feed is a cracked gasoline fraction boiling essentially within the range of F. and 232 F. the aromaticfree raffinate is advantageously passed via line I3 to a fractionator I4 where it is fractionated to recover an overhead fraction boiling essentially between 185 F. and about 210 F. and a higher bottom fraction. The higher boiling bottom fraction is removed via line l5 as a product of the process. The non-hydroaromatic fraction taken overhead is subjected to a catalytic isomerization vantageously passed via line l5 to a fractionator I6 to effect a further concentration of the desired hydroaromatic naphthenes. Thus, for eX- ample, in the above-assumed case the isomerized product is advantageously separated in fractionator I6 into a higher boiling fraction boiling above about 210 F. and containing substantially all of the hydroaromatic naphthenes, and a lower boiling fraction containing unisomerized naphthenes and other non-naphthenic constituents. A portion of this lower boiling fraction may be advantageously recycled via line I1 to the isomerization step and the remainder may be withdrawn via line I8 as a product of the process. The isomerized product is cycled by line 6 and added to theolenic feed stock after the first hydrogen treatment and prior to the second hydrogen treatment.

The process of the invention, it is seen, allows' the production of aromatic hydrocarbons (if desired in a substantially pure state) from cracked gasolinas and other sulfur-bearing 'olefinic petroleum fractions. This is made possible by the particular order and combination of the steps described. Some of the fine points contributing to this desired end may be mentioned. The combination of the first, or low temperature, hydrogen treatment and the diluting effect of the recycled isomerized material acts to reduce the sulfur content of the material to the second, or high temperature, hydrogen treatment to below about 0.10%. The diluting effect of the isomerized material makes aless drastic treatment in the iirst hydrogen treatment necessary in order to reduce the sulfur content to'0.10% 'or below. This in turn allows the rst hydrogen treatment to be carried out with less hydrogenation of olens. The preservation of the oleins in the rst step is desired because the hydrogenation of these olens in the second, or high temperature, step is desired to oiset or counterbalance the large endothermic heat of reaction involved in the production of the aromatics. In the first, or low temperature, hydrogen treatment and also to some extent in the second, or high temperature, hydrogen treatment, there is a tendency for a part of the hydroaromatic naphthenes in the feed to isomerize to non-hydroaromatic naphthenes. In the process described these materials are reisomerized and recycled, thereby avoiding loss through thisl course. The isomerization step in the present process is also improved since the hydroaromatic naphthenes are dehydrogenated and removed prior to the isomerization. They therefore do not repress the desired isomeriza- 6 tion as they do when the isomerization is applied prior to the dehydrogenation. I claim as my invention: 1. A process for the production of aromatic hydrocarbons from sulfur-bearing olefnic petroleum fractions which comprises treating said petroleum fractions with hydrogen at a temperature between about '450 F. and 850 F. in the presence of a sulf-active hydrogenation catalyst under conditions selected to reduce the sulfur content lof the material with incomplete hydrogenation of olens; admixing with the product of said treatment a saturated isomerized hydroaromatic fraction mentioned below to produce a mixture containing less than about 0.10% sulfur; treating the mixture with hydrogen at a temperature between about 850 F. and 1000 F. in the presence of a dehydrogenating sulfide of a metal of the iron group under conditions chosen to effect further desulfurization, dehydrogenation of naphthenes and a substantial saturation of oleiins; removing aromatic products from the thustreated material; fractionating the remainder to separate a fraction rich in non-hydroaromatic naphthenes; subjecting said non-hydroaromatic fractions to a catalytic isomerization treatment to'convert non-hydroaromatic naphthenes to hydroaromatic naphthenes; and cycling at least a portion of said isomerized material to the second hydrogen treatment as above specified.

2. Process according to claim 1 in which the first hydrogen treatment is adjusted to reduce the sulfur contentV of the feed to about 0.10%.

3. Process according to claim 1 in which the catalyst used in the second hydrogen treatment comprises nickel sulde.

4. Process according to claim 1 in which the catalyst used in the second hydrogen treatment consists essentially of nickel sulde and tungsten sulde.

5. Process according to claim 1 in which the fraction treated boils predominantly within the range of F. and 232 F. and the predominant aromatic product is toluene.

ROBERT M. COLE.

REFERENCES CTED.

The following references are' of record in .the le of this patent: f

UNITED STATES PATENTS l. Date Number Name 2,298,346 Corson et ai. Oct. 13, 1942 2,241,393 Danner...-.. May 13, 1941 2,283,854 Friedman et al. ---1-.. May 19, 1942 2,288,866 Hoog July v'1, 1942 2,374,175 Burk Apr. 24, 1945 2,348,557 Mattox May 7, 1944 2,355,366 Conn 1...---- Aug. 8, 1944 2,376,086 Reid May 15, 1945 FOREIGN PATENTS Number Country Date 296,429 Great Britain ,---1 Dec. 16, 1929 Great Britain Nov. 2, 1934 

